Correlation of absolute temperature coefficients of ultrasonic velocity in solutions of dilute coal and lignite extracts with molecular masses

Absolute temperature coefficients of ultrasonic velocity b were determined from temperature dependences of the velocity of the longitudinal ultrasonic waves with frequency 2.5 MHz in solutions of pyridine and tetrahydrofuran extracts, obtained from lignite and coals of different ranks (54.1–85.6 wt% of carbon). The relationship between absolute temperature coefficients b of all extract solutions and extract molecular masses M was studied. It was stated that the dependence of b√M vs. M deviates considerably from the rule b√M=const, found empirically by Lagemann et al. for pure organic liquids. Experimental data for lignite and coal product solutions were best fitted by the equation b√M=AM+B, where constants A and B were determined from the fits having the correlation coefficients r within the range 0.99–0.999. This empirical formula was applied to determine the molecular mass of a sample, for which the Knauer osmometer method could not be used.